SEM and TEM Studies of Magnetic Shape Memory NiCoMnIn Melt Spun Ribbons

Abstract

Microstructure of Ni50-xCoxMn35.5In14.5 (x=0, 3, 5) melt-spun ribbons was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The typical layered microstructure consisting of oriented columnar grains and colonies of fine equi-axed grains was observed in the cross section of ribbons. The crystallographic structure of ribbons varied with the content of Co in alloys what affected of their Ms temperature. For the x=0 the single phase of monoclinic 14M modulated martensite was observed, but for x=3 and 5, a two phase structure of L21 austenite and monoclinic 14M or orthorhombic 10M modulated martensite were identified. Different temperature range of martensitic transformations were explained basing on valence electron concentration per atom e/a versus Ms relationship.